Linear Fresnel lens

Abstract

By scattering the noise light generated by the rise surface over a wide area, the intensity of the noise light is reduced. [Solution] The linear Fresnel lens 1 comprises a base material 2 and a linear Fresnel lens structure 3 formed on at least one surface of the base material 2. The linear Fresnel lens structure 3 includes a plurality of Fresnel lens surfaces 4 extending along the X direction and arranged in the Y direction, and a recessed structure 10 formed on a rise surface 5 connecting adjacent Fresnel lens surfaces 4, 4 in the Y direction. The recessed structure 10 has a plurality of protrusions 12 repeatedly provided on the rise surface 5 along the X direction at a predetermined pitch P. The protrusions 12 include a first diffusion surface 14 connected to the upper edge 4a of one of the adjacent Fresnel lens surfaces 4, 4 in the Y direction and inclined with respect to the XY plane, and a second diffusion surface 16 connecting the lower edge 4b ​​of the other second Fresnel lens surface 4 and the first diffusion surface 14.

Description

Technical Field

[0001] The present invention relates to a linear Fresnel lens.

Background Art

[0002] A Fresnel lens is an optical element having a lens structure with a sawtooth-shaped cross-section. The Fresnel lens has functions such as diffusing, condensing, or refracting light, for example. The Fresnel lens includes a plurality of Fresnel lens surfaces having a lens function and a rise surface (non-lens surface) connecting adjacent Fresnel lens surfaces. The Fresnel lens is used by making light enter therein. At this time, however, light may leak out from the rise surface connecting the Fresnel lens surfaces and become noise light. For this reason, there are problems that the optical image projected from the Fresnel lens becomes blurred, or ghost images or color unevenness occur.

[0003] In order to suppress such noise light, for example, Patent Document 1 describes that by making the rise surface (non-lens surface) of the Fresnel lens an uneven surface having a sawtooth-shaped cross-section, internal reflected light is not emitted outside from the rise surface and is confined inside the lens. Further, Patent Document 2 describes that a light absorption layer provided on the rise surface of the Fresnel lens sheet absorbs unnecessary light and prevents the generation of ghost images due to the unnecessary light leaking out from the rise surface.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, the uneven surface of the rise surface (non-lens surface) in Patent Document 1 is constructed by arranging small corner cubes closely packed in the height direction, and has an uneven structure consisting of multiple grooves extending along the longitudinal direction of the rise surface (see Figure 17). However, although the uneven structure of the rise surface in Patent Document 1 can suppress noise light leakage from the rise surface to some extent, it cannot completely confine the noise light within the lens. As a result, the noise light leaking from the Fresnel lens is concentrated and emitted in a specific direction, resulting in the problem that the intensity of the noise light in the projected optical image is still high (see Figure 20).

[0006] Furthermore, the uneven surface structure of the rise surface described in Patent Document 1 has an undercut structure in which the lower concave structure is hidden behind the upper convex structure of the rise surface. Therefore, there is a manufacturing problem in that it is difficult to form the uneven surface structure as designed because the upper convex structure of the rise surface hinders the formation of the concave structure below it. In particular, in manufacturing methods that form the uneven surface structure from the front side in the optical axis direction of the Fresnel lens, such as photolithography using a laser writing device or cutting, it has been impossible or extremely difficult to form an uneven surface structure with an undercut structure like that of Patent Document 1. In addition, although it is possible to form the uneven surface structure on the lower side of the rise surface by tilting the rise surface of Patent Document 1, tilting the rise surface can cause stray light generation, which may degrade the final optical performance of the Fresnel lens.

[0007] Furthermore, in Patent Document 2, a light-absorbing agent is applied to the rise surface of the Fresnel lens sheet to form a light-absorbing layer (see Figure 18). However, even if a light-absorbing layer like that in Patent Document 2 is applied to the rise surface, it is not possible to sufficiently prevent the leakage of noise light from the rise surface, and the leaked noise light is concentrated and emitted in a specific direction, resulting in the problem that the intensity of noise light in the projected optical image remains high (see Figure 21). In addition, there are problems such as paint overflowing from the rise surface onto the Fresnel lens surface, or insufficient coating at the edges of the rise surface, which can lead to manufacturing defects of the Fresnel lens and a decrease in optical performance.

[0008] Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to provide a linear Fresnel lens that can reduce the intensity of noise light by scattering noise light generated by the rise surface over a wide area. [Means for solving the problem]

[0009] To solve the above problems, according to one aspect of the present invention, Substrate and A linear Fresnel lens structure formed on at least one surface of the substrate, Equipped with, Assuming the surface of the substrate is the XY plane and the thickness direction of the substrate is the Z direction, The linear Fresnel lens structure described above is Multiple Fresnel lens surfaces extending along the X direction and arranged in the Y direction, An uneven structure formed on the rise surface connecting adjacent Fresnel lens surfaces in the Y direction, Includes, The aforementioned uneven structure has a plurality of protrusions that are repeatedly provided on the rise surface at a predetermined pitch along the X direction, The aforementioned protrusion is, A first diffusion surface is connected to the upper edge of one of the adjacent Fresnel lens surfaces in the Y direction and is inclined with respect to the XY plane, A second diffusion surface connecting the lower edge of the other second Fresnel lens surface among the adjacent Fresnel lens surfaces in the Y direction and the first diffusion surface, A linear Fresnel lens is provided, including the following.

[0010] The first diffusing surface may be configured to diffuse light incident on the first diffusing surface in at least multiple directions within the YZ plane.

[0011] The first diffusing surface may be configured to diffuse light incident on the first diffusing surface in multiple directions within the YZ plane and multiple directions within the XY plane.

[0012] The first diffusing surface may be formed of a spherical or aspherical curved surface.

[0013] The first diffusing surface may be formed of a convex lens-like curved surface.

[0014] The second diffusing surface may diffuse the light incident on the second diffusing surface in a plurality of directions within the XY plane.

[0015] The boundary line between the first diffusing surface and the second diffusing surface is an arcuate curved line, The second diffusing surface may be formed of a cylindrical lens surface along the arcuate curved line.

[0016] The boundary line between the first diffusing surface and the second diffusing surface is a broken line formed of a part of a polygon, The second diffusing surface may be formed of a convex surface combining a plurality of flat surfaces along the broken line.

[0017] The inclination angle of the first diffusing surface with respect to the XY plane may be larger than the inclination angle of the Fresnel lens surface with respect to the XY plane.

[0018] The linear Fresnel lens includes a prism sheet having a prism structure as the linear Fresnel lens structure, The plurality of Fresnel lens surfaces of the prism structure may be planes inclined at substantially the same inclination angle.

Advantages of the Invention

[0019] According to the present invention, the intensity of the noise light can be reduced by scattering the noise light generated by the rise surface over a wide range.

Brief Description of the Drawings

[0020] [Figure 1]These are a perspective view and a side view showing the schematic configuration of a linear Fresnel lens according to the first embodiment of the present invention. [Figure 2] These are perspective and side views showing the schematic configuration of a linear Fresnel lens according to a modified example of the same embodiment. [Figure 3] This is a magnified cross-sectional view showing a conventional Fresnel lens. [Figure 4] This is an explanatory diagram showing the simulation results using a conventional linear Fresnel lens. [Figure 5] This is a perspective view showing a linear Fresnel lens according to a first embodiment of the present invention. [Figure 6] This is a plan view showing a linear Fresnel lens according to the same embodiment. [Figure 7] This is a front view showing a linear Fresnel lens according to the same embodiment. [Figure 8] A side view showing a linear Fresnel lens according to the same embodiment. [Figure 9] These are YZ cross-sectional views (Figure 9A) and XY cross-sectional views (Figure 9B) showing the linear Fresnel lens structure of a conventional linear Fresnel lens. [Figure 10] Figure 10A shows a YZ cross-sectional view of the linear Fresnel lens structure of a linear Fresnel lens according to the first embodiment of the present invention, Figure 10B shows an XY cross-sectional view at the height of the inclined diffusion surface, and Figure 10C shows an XY cross-sectional view at the height of the vertical diffusion surface. [Figure 11] This is a perspective view showing a linear Fresnel lens according to a second embodiment of the present invention. [Figure 12] This is a plan view showing a linear Fresnel lens according to the same embodiment. [Figure 13] This is a front view showing a linear Fresnel lens according to the same embodiment. [Figure 14] A side view showing a linear Fresnel lens according to the same embodiment. [Figure 15] Figure 15A shows a YZ cross-sectional view of the linear Fresnel lens structure according to the same embodiment, Figure 15B shows an XY cross-sectional view at the height of the inclined diffusion surface, and Figure 15C shows an XY cross-sectional view at the height of the vertical diffusion surface. [Figure 16] This is a perspective view showing a linear Fresnel lens according to Comparative Example 1. [Figure 17] This is a perspective view showing a linear Fresnel lens according to Comparative Example 2. [Figure 18] This is a perspective view showing a linear Fresnel lens according to Comparative Example 3. [Figure 19] This is a photograph showing the simulation results of the light intensity distribution related to Comparative Example 1. [Figure 20] This is a photograph showing the simulation results of the light intensity distribution related to Comparative Example 2. [Figure 21] This is a photograph showing the simulation results of the light intensity distribution related to Comparative Example 3. [Figure 22] This is a photograph showing the simulation results of the light intensity distribution according to Example 1. [Figure 23] This is a photograph showing the simulation results of the light intensity distribution according to Example 2. [Modes for carrying out the invention]

[0021] Embodiments of the present invention will be described in detail below with reference to the attached drawings. The specific dimensions, materials, numerical values, etc., shown in these embodiments are merely examples to facilitate understanding of the invention and do not limit the present invention unless otherwise specified. In this specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals to avoid redundant explanations, and elements not directly related to the present invention are omitted from the illustrations.

[0022] [1. Overview of Linear Fresnel Lenses] First, an overview of the linear Fresnel lens 1 according to the first embodiment of the present invention will be described with reference to Figures 1 and 2. Figure 1 is a perspective view and a side view showing the schematic configuration of the linear Fresnel lens 1 according to this embodiment. Figure 2 is a perspective view and a side view showing the schematic configuration of the linear Fresnel lens 1 according to a modified example of this embodiment. For the sake of explanation, the illustration of the uneven structure 10 (see Figure 5, etc.) provided on the rise surface 5 of the linear Fresnel lens 1 according to this embodiment has been omitted in Figures 1 and 2.

[0023] As shown in Figures 1 and 2, the linear Fresnel lens 1 is a thin, sheet-like optical element equipped with a convex and concave structure (linear Fresnel lens structure 3) having a sawtooth-shaped cross-section. The linear Fresnel lens 1 has a function to control the light incident on it, such as the function to diffuse, focus, or refract the light.

[0024] For example, the linear Fresnel lens 1 shown in Figure 1 has the function of refracting light, refracting parallel light 50 (collimated light) incident from a surface light source at a predetermined refraction angle and emitting normal light 51 from the refracted parallel light. The linear Fresnel lens 1 shown in Figure 2 also has the function of focusing light, focusing the parallel light 50 incident from a surface light source and emitting normal light 51. Furthermore, with the linear Fresnel lens 1 shown in Figure 2, it is also possible to diffuse light incident from a point light source by reversing the direction of light incidence to the linear Fresnel lens 1.

[0025] The applications of the linear Fresnel lens 1 according to this embodiment will now be described. For example, the linear Fresnel lens 1 shown in Figure 1 may have a light refraction function like a prism. Due to this refraction function, the linear Fresnel lens 1 can be used as an optical element that bends the optical axis of incident light, for example. The linear Fresnel lens 1 shown in Figure 2 may also have a function that diffuses light incident from a line light source. Due to this diffusion function, the linear Fresnel lens 1 can be used as an illumination lens for an LED, for example. The linear Fresnel lens 1 shown in Figure 2 may also have a function that focuses incident light into a slit-shaped beam of light. Due to this focusing function, the linear Fresnel lens 1 can be used as a sunlight focusing lens, for example.

[0026] Next, the schematic configuration of the linear Fresnel lens 1 will be described. As shown in Figures 1 and 2, the linear Fresnel lens 1 comprises, for example, a flat substrate 2 and a linear Fresnel lens structure 3 formed on at least one surface of the substrate 2.

[0027] For the purpose of explaining the configuration of the linear Fresnel lens 1, the following assumptions are made regarding the X, Y, and Z directions: The X and Y directions are plane directions parallel to the surface of the substrate 2 of the linear Fresnel lens 1 and are perpendicular to each other. The Z direction is the thickness direction of the substrate 2 (i.e., the optical axis direction of the linear Fresnel lens 1). The Z direction is perpendicular to the sum of the X and Y directions. The XY plane is a plane parallel to the surface of the substrate 2 of the linear Fresnel lens 1. The XZ plane and YZ plane are planes perpendicular to the surface of the substrate 2. The XY plane, XZ plane and YZ plane are perpendicular to each other.

[0028] The base material 2 is, for example, a sheet-shaped (flat) lens base material. The base material 2 is formed from a transparent material that is transparent to light in at least the visible light wavelength range. For example, the base material 2 may be formed from an inorganic material such as glass, or an organic material such as various resins. The planar shape (projected onto the XY plane) of the base material 2 in the example shown in Figures 1 and 2 is rectangular, but the base material 2 is not limited to this example, and the planar shape of the base material 2 may be any other shape, such as a circle, an ellipse, a polygon, or a strip. Furthermore, the three-dimensional shape of the base material 2 is not limited to a sheet shape, but may be a block shape, for example.

[0029] The linear Fresnel lens structure 3 is a convex-convex structure that realizes a predetermined lens function (e.g., refraction, focusing, diffusion, etc.) of the linear Fresnel lens 1. The cross-sectional shape of the linear Fresnel lens structure 3 in the YZ plane is sawtooth-shaped, and the cross-sectional shape in the XZ plane is linear. The linear Fresnel lens structure 3 has a plurality of Fresnel lens surfaces 4 and a plurality of rise surfaces 5 (non-lens surfaces).

[0030] In the examples shown in Figures 1 and 2, the linear Fresnel lens structure 3 is formed on only one surface of the substrate 2, while the other surface (back surface) of the substrate 2 is a flat surface. However, the linear Fresnel lens of the present invention is not limited to this example, and for example, the same or different linear Fresnel lens structures 3 may be formed on both surfaces (i.e., the front and back surfaces) of the substrate 2. Alternatively, the linear Fresnel lens structure 3 may be formed on one surface of the substrate 2, and another lens structure may be formed on the other surface (back surface) of the substrate 2.

[0031] The Fresnel lens surface 4 is the lens surface of the linear Fresnel lens 1 that has a lens function. The Fresnel lens surface 4 is the lens surface that realizes the predetermined lens function of the linear Fresnel lens 1 and functions as a light control surface that controls light. The Fresnel lens surface 4 is an inclined surface that extends along the X direction on the surface (XY plane) of the substrate 2 and is inclined at a predetermined inclination angle θ with respect to the XY plane. The inclined Fresnel lens surface 4 in this way may be a plane extending in the X direction, or it may be a curved surface such as a cylindrical lens surface (for example, a cylindrical convex surface or a cylindrical concave surface) extending in the X direction. Multiple Fresnel lens surfaces 4 are arranged at a predetermined pitch in the Y direction and all extend parallel to the X direction.

[0032] The rise surface 5 is a non-lens surface of the linear Fresnel lens 1 that does not have a lens function. The rise surface 5 functions as a connecting surface that connects two adjacent Fresnel lens surfaces 4, 4 in the Y direction. The rise surface 5 extends along the X direction on the surface (XY plane) of the substrate 2. Multiple rise surfaces 5 are arranged at a predetermined pitch in the Y direction and all extend parallel to the X direction.

[0033] The rise surface 5 is preferably a plane perpendicular to the XY plane (i.e., a plane parallel to the Z direction, which is the optical axis direction), and the inclination angle θ' of the rise surface 5 with respect to the XY plane is preferably 90°. This allows the rise surface 5 to be positioned so that it interferes as little as possible with light incident or emitted in the optical axis direction (Z direction), thereby improving the performance of the linear Fresnel lens 1. However, due to manufacturing constraints of the linear Fresnel lens structure 3, the rise surface 5 may be a plane inclined with an inclination angle θ' of, for example, 70° or more, preferably 80° or more, with respect to the XY plane.

[0034] Furthermore, the rise surface 5 of the linear Fresnel lens 1 according to this embodiment has an uneven surface structure 10 (see Figure 5, etc.) which will be described later, and the details of this structure will be described later.

[0035] In the linear Fresnel lens 1 shown in Figure 1, the Fresnel lens surface 4 is a strip-shaped plane extending in the X direction. Multiple Fresnel lens surfaces 4 have the same shape as each other and are inclined with respect to the XY plane at the same inclination angle θ. As a result, the linear Fresnel lens structure 3 of the linear Fresnel lens 1 shown in Figure 1 functions as a prism structure, refracting the incident parallel light 50 at a predetermined angle and emitting the refracted parallel light (normal light 51). Thus, the linear Fresnel lens 1 shown in Figure 1 is configured as a prism sheet with a prism structure as the linear Fresnel lens structure 3.

[0036] On the other hand, in the linear Fresnel lens 1 shown in Figure 2, the multiple Fresnel lens surfaces 4 are inclined with respect to the XY plane at mutually different inclination angles θ. The inclination angles θ of the multiple Fresnel lens surfaces 4 increase from the center (inside) in the Y direction to the outside. As a result, the angle of refraction of light by the Fresnel lens surface 4 becomes larger for Fresnel lens surfaces 4 that are located further out than the center (inside) in the Y direction. Thus, the linear Fresnel lens 1 shown in Figure 2 is a lens in which the thickness of the lens is reduced by dividing the lens surface of a spherical lens such as a cylindrical lens into multiple regions (multiple Fresnel lens surfaces 4). As a result, the linear Fresnel lens 1 shown in Figure 2 can perform functions such as focusing and diffusing light, similar to spherical lenses such as cylindrical lenses.

[0037] Furthermore, the multiple Fresnel lens surfaces 4 of the linear Fresnel lens 1 shown in Figures 1 and 2 may be spherical surfaces having a constant radius of curvature from the optical axis center to the periphery in the Y direction, like a cylindrical lens, or they may be aspherical surfaces in which the radius of curvature changes from the optical axis center to the periphery in the Y direction.

[0038] As described above, the linear Fresnel lens 1 according to this embodiment is a general term for a sheet-shaped optical element. The linear Fresnel lens structure 3 of the linear Fresnel lens 1 has an uneven structure consisting of a plurality of grooves extending linearly in one direction (X direction), and its cross-sectional shape (cross-section in the YZ plane) is sawtooth-shaped. Compared to lens elements having a general spherical or aspherical lens surface (e.g., cylindrical lenses, prisms, etc.), the linear Fresnel lens 1 equipped with such a linear Fresnel lens structure 3 can be made thinner.

[0039] The linear Fresnel lens 1 according to this embodiment has, for example, a prism function that refracts light as shown in Figure 1, or a cylindrical lens function that focuses or diffuses light as shown in Figure 2. For example, the linear Fresnel lens 1 has the function of refracting, focusing, or diffusing light in only one direction (Y direction) of the surface direction of the lens surface (XY plane), and does not refract, focus, or diffuse light in other directions (e.g., the X direction). A linear Fresnel lens 1 with such characteristics can, for example, diffuse slit light with a long X-direction incident from a line light source in the Y-direction to emit diffuse light having a rectangular shape in the XY plane, or focus parallel light from a surface light source in the Y-direction to emit slit light with a long X-direction.

[0040] [2. Challenges of conventional linear Fresnel lenses] Next, with reference to Figures 3 and 4, the challenges of noise light in the conventional linear Fresnel lens 100 will be explained. Figure 3 is an enlarged cross-sectional view showing the conventional linear Fresnel lens 100. Figure 4 is an explanatory diagram showing the simulation results using the conventional linear Fresnel lens 100.

[0041] As shown in Figures 3 and 4, the conventional linear Fresnel lens 100 has a prism structure with a sawtooth cross-section as the linear Fresnel lens structure 103 on the lens surface. The prism structure, which is the conventional linear Fresnel lens structure 103, has a plurality of Fresnel lens surfaces 104 and a rise surface 105. The uneven shape of the plurality of Fresnel lens surfaces 104 and the rise surface 105 of the conventional linear Fresnel lens structure 103 is the same as the uneven shape of the plurality of Fresnel lens surfaces 4 and the rise surface 5 (see Figure 1) of the linear Fresnel lens structure 3 according to the first embodiment.

[0042] As shown in Figure 3, the rise surface 105 of the conventional linear Fresnel lens 100 is a flat surface parallel to the optical axis direction (Z direction), and the rise surface 105 does not have a special uneven structure 10 (see Figure 5, etc.) like the rise surface 5 of the linear Fresnel lens 1 according to the first embodiment. Therefore, in the conventional linear Fresnel lens 100, a portion of the light refracted by the Fresnel lens surface 104 is specularly reflected by the flat rise surface 105, generating noise light 52. The noise light 52 is emitted in a concentrated direction different from the normal light 51 that is normally refracted by the Fresnel lens surface 104.

[0043] As a result, as shown in the simulation results in Figure 4, multiple linear noise rays 52 are significantly generated on the screen 62 onto which the optical image emitted from the conventional linear Fresnel lens 100 is projected, separate from the rectangular illumination area of ​​normal light 51. In detail, as shown in Figure 4, when parallel light 50 emitted from the light source 60 is incident on the conventional linear Fresnel lens 100, most of the parallel light 50 is refracted at the Fresnel lens surface 104 and becomes normal light 51 traveling in the desired direction. However, a portion of the incident parallel light 50 is specularly reflected by the flat rise surface 105 and becomes noise light 52 traveling in a direction different from that of the normal light 51. As a result, in the optical image projected onto the screen 62, multiple linear noise rays 52 appear with high intensity in areas far from the rectangular illumination area of ​​normal light 51.

[0044] Thus, in conventional linear Fresnel lenses 100 (for example, prism sheets with a prism structure), noise light 52 is generated in the same direction due to reflection or refraction of incident light on the flat rise surface 105, and because this noise light 52 is concentrated at a predetermined location on the screen 62, there is a problem that the intensity of the noise light 52 becomes high.

[0045] Therefore, in order to solve the above problem, the linear Fresnel lens 1 according to this embodiment aims to sufficiently reduce the intensity of noise light 52 by scattering the noise light 52 generated by the rise surface 5 of the linear Fresnel lens structure 3 over a wide area. For this purpose, the linear Fresnel lens 1 according to this embodiment is characterized by having a special uneven structure 10 (see Figure 5, etc.) on the rise surface 5 of the linear Fresnel lens structure 3. The uneven structure 10 of the rise surface 5, which is a feature of the linear Fresnel lens structure 3 according to this embodiment, will be described in detail below.

[0046] [3. Configuration of the Fresnel lens according to the first embodiment] Next, the configuration of the linear Fresnel lens 1 according to the first embodiment of the present invention will be described with reference to Figures 5 to 8. Figures 5 to 8 are a perspective view, a plan view, a front view, and a side view, respectively, showing the linear Fresnel lens 1 according to the first embodiment.

[0047] [3.1. Basic Configuration of Fresnel Lenses] As shown in Figures 5 to 8, the linear Fresnel lens 1 according to the first embodiment comprises a base material 2 and a linear Fresnel lens structure 3 formed on at least one surface of the base material 2. The linear Fresnel lens structure 3 is an uneven structure having a sawtooth cross-sectional shape. The linear Fresnel lens structure 3 comprises a plurality of Fresnel lens surfaces 4, a plurality of rise surfaces 5, and an uneven structure 10 formed on each rise surface 5. The plurality of Fresnel lens surfaces 4 and the plurality of rise surfaces 5 are arranged alternately in the Y direction, forming a striped arrangement.

[0048] The Fresnel lens surface 4 is the lens surface that performs the original lens function of the linear Fresnel lens 1. The Fresnel lens surface 4 is a band-shaped inclined surface that extends linearly in the X direction. Multiple Fresnel lens surfaces 4 are regularly arranged in the Y direction at a predetermined pitch Py, and the multiple Fresnel lens surfaces 4 extend in directions parallel to each other (the X direction).

[0049] The Fresnel lens surface 4 may be a flat surface or a spherical or aspherical curved surface (e.g., a cylindrical convex or cylindrical concave surface), depending on the function to be provided to the linear Fresnel lens 1. For example, if the linear Fresnel lens 1 is to be provided with a light refraction function, the Fresnel lens surface 4 may be a flat surface. If the linear Fresnel lens 1 is to be provided with a light diffusion or focusing function, the Fresnel lens surface 4 may be a curved surface. Furthermore, the inclination angle θ of the Fresnel lens surface 4 with respect to the XY plane is preferably greater than 0° and less than 90°, and between 10° and 80°. The inclination angles θ of multiple Fresnel lens surfaces 4 may be the same to each other (see Figure 1) or different to each other (see Figure 2).

[0050] The rise surface 5 has the function of connecting two adjacent Fresnel lens surfaces 4, 4 in the Y direction. More specifically, the rise surface 5 connects the upper edge 4a of one of the two adjacent Fresnel lens surfaces 4, 4 (the first Fresnel lens surface) to the lower edge 4b ​​of the other Fresnel lens surface 4 (the second Fresnel lens surface). Thus, the rise surface 5 functions as a connecting surface for linking two adjacent Fresnel lens surfaces 4, 4 and is a non-lens surface that does not perform the original lens function of the linear Fresnel lens 1.

[0051] [3.2. Uneven structure of the rise surface] In the linear Fresnel lens 1 according to this embodiment, a special uneven structure 10 is formed on the rise surface 5, characterized in that the rise surface 5 is an uneven surface rather than a flat surface. This uneven structure 10 on the rise surface 5 is composed of a repeating pattern of multiple protrusions 12 arranged in the longitudinal direction (X direction) of the rise surface 5, and is, for example, an uneven pattern on the order of micrometers (1 to 1000 μm). This uneven structure 10 has the function of diffusing and scattering noise light generated on the rise surface 5 over a wide area. Due to the diffusion and scattering function of this uneven structure 10, the noise light can be dispersed over a wide area in the optical image projected from the linear Fresnel lens 1, thereby reducing the intensity of the noise light. Thus, the uneven structure 10 provided on the rise surface 5 according to this embodiment functions as a noise light reduction structure.

[0052] The uneven surface structure 10 has a plurality of protrusions 12 that are repeatedly provided on the rise surface 5 along the X direction at a predetermined pitch P. The protrusions 12 are fine protrusions that project in the Y direction from the rise surface 5 (ideally a vertical surface perpendicular to the XY plane). The protrusions 12 have a shape that is symmetrical with respect to the X direction. From the viewpoint of facilitating the design and manufacture of the uneven surface structure 10, it is preferable that the plurality of protrusions 12 constituting the uneven surface structure 10 have the same shape as each other, but they may have different shapes. The pitch P of the protrusions 12 that are repeatedly arranged in the X direction corresponds to the width of one protrusion 12 in the X direction.

[0053] The convex portion 12 is formed over the entire height direction (Z direction) of the rise surface 5. That is, the height H of the convex portion 12 is approximately the same as the height of the rise surface 5. The upper part of the convex portion 12 in the Z direction is connected to the upper edge 4a of one of the two adjacent Fresnel lens surfaces 4, 4 in the Y direction, the first Fresnel lens surface 4. The lower part of the convex portion 12 in the Z direction is connected to the lower edge 4b ​​of the other of the two Fresnel lens surfaces 4, 4, the second Fresnel lens surface 4.

[0054] The convex portion 12 comprises at least one inclined diffusion surface 14 (first diffusion surface) and at least one vertical diffusion surface 16 (second diffusion surface). In other words, the surface of one convex portion 12 includes at least one inclined diffusion surface 14 and at least one vertical diffusion surface 16. The inclined diffusion surface 14 is provided on the upper side of the convex portion 12 and is an inclined surface that has the function of diffusing light (especially noise light). On the other hand, the vertical diffusion surface 16 is provided on the lower side of the convex portion 12 and is a vertical surface that has the function of diffusing light. The configurations of the inclined diffusion surface 14 and the vertical diffusion surface 16 will be described in detail below.

[0055] [3.3. Inclined Diffusion Surface] The inclined diffusion surface 14 is an example of a first diffusion surface. The inclined diffusion surface 14 is an inclined surface provided on the upper part of the convex portion 12 in the Z direction, and forms the upper surface of the convex portion 12. The upper end of the inclined diffusion surface 14 is connected to the upper edge 4a of one of the adjacent Fresnel lens surfaces 4, 4 in the Y direction, which is the first Fresnel lens surface 4 (the right Fresnel lens surface 4 in Figure 8). The lower end of the inclined diffusion surface 14 is connected to the upper part of the vertical diffusion surface 16.

[0056] The inclined diffusion surface 14 is an inclined surface that is inclined in the opposite direction to the Fresnel lens surface 4 with respect to the XY plane. For example, as shown in Figures 5 and 8, if the Fresnel lens surface 4 is inclined downwards in the positive direction of the Y, the inclined diffusion surface 14 will be inclined downwards in the negative direction of the Y.

[0057] The inclination angle α of the inclined diffusion surface 14 with respect to the XY plane (see Figure 8) is greater than 0° and less than 90°, preferably 60° or more, more preferably 70° or more, and even more preferably 80° or more and less than 90°. The larger the inclination angle α of the inclined diffusion surface 14 and the closer it is to 90°, the smaller the amount of protrusion (thickness D of the protrusion 12) of the convex portion 12 protruding in the Y direction from the rise surface 5 can be, thereby reducing the area of ​​the convex portion 12 (i.e., the area of ​​the inclined diffusion surface 14) in the XY plane view. Therefore, the amount of light in the optical axis direction (Z direction) that is directly incident on the inclined diffusion surface 14 can be reduced, and the generation of noise light due to light directly incident on the inclined diffusion surface 14 can be suppressed.

[0058] As shown in Figure 8, if the inclined diffusion surface 14 is a curved surface, the inclination angle α of the inclined diffusion surface 14 represents the angle between the imaginary straight line connecting the upper and lower ends of the inclined diffusion surface 14 and the XY plane.

[0059] As shown in Figure 6, in an XY plan view of the convex portion 12, the inclined diffusion surface 14 has a planar shape that combines an arc-shaped curved line, such as a circular arc, and a straight line. Specifically, the boundary line between the upper edge of the inclined diffusion surface 14 (the contour line of the upper end in the Z direction) and the upper edge 4a of the first Fresnel lens surface 4 is a straight line. On the other hand, the boundary line 15 between the lower edge of the inclined diffusion surface 14 (the contour line of the lower end in the Z direction) and the vertical diffusion surface 16 is an arc-shaped curved line. Preferably, the boundary line 15 between the inclined diffusion surface 14 and the vertical diffusion surface 16 is an arc-shaped curved line, and preferably the radius of curvature of the arc of the boundary line 15 is the same as the radius of curvature of the cylindrical lens surface of the vertical diffusion surface 16. This allows the inclined diffusion surface 14 to be appropriately connected to the vertical diffusion surface 16, which is made up of a cylindrical lens surface, as will be described later. Furthermore, the boundary line 15 between the inclined diffusion surface 14 and the vertical diffusion surface 16 is not limited to the example of a curved line in the shape of a circular arc, but may be, for example, an elliptical curved line or a curved line of other shapes.

[0060] The inclined diffusion surface 14 is preferably a spherical or aspherical curved surface. In the examples shown in Figures 5 to 8, the inclined diffusion surface 14 is a convex lens-like curved surface made of an upwardly convex sphere, but it may also be a downwardly convex concave lens-like curved surface. By forming the inclined diffusion surface 14 as a spherical or aspherical curved surface in this way, a lens effect can be imparted to the inclined diffusion surface 14, thereby improving the diffusion effect of noise light by the inclined diffusion surface 14.

[0061] The gradient diffusion surface 14 diffuses the noise light incident on it, scattering it three-dimensionally in multiple directions in the YZ plane and multiple directions in the XY plane (see Figures 10A and 10B). Therefore, the gradient diffusion surface 14 can disperse the noise light three-dimensionally over a wide area, thereby effectively reducing the intensity of the noise light.

[0062] The inclined diffusion surface 14 is not limited to the curved surface example described above; for example, it may be a flat surface inclined with respect to the XY plane. In this case, noise light can be diffused by the inclined diffusion surface 14 and the vertical diffusion surface 16, which have different inclination angles α and β, and dispersed two-dimensionally in multiple directions within the YZ plane and the XY plane.

[0063] [3.4. Vertical Diffusion Surface] The vertical diffusion surface 16 is an example of a second diffusion surface. The vertical diffusion surface 16 is a vertical surface provided on the lower side of the convex portion 12. The vertical diffusion surface 16 connects the inclined diffusion surface 14 to the lower edge 4b ​​of the other second Fresnel lens surface 4 (the Fresnel lens surface 4 on the left in Figure 8) of the two adjacent Fresnel lens surfaces 4, 4 in the Y direction. The lower end of the vertical diffusion surface 16 is connected to the lower edge 4b ​​of the second Fresnel lens surface 4. The upper end of the vertical diffusion surface 16 is connected to the lower end of the inclined diffusion surface 14. The boundary line 15 between the inclined diffusion surface 14 and the vertical diffusion surface 16 is a ridge line.

[0064] The vertical diffusion surface 16 is preferably a curved surface substantially perpendicular to the XY plane. That is, the inclination angle β of the vertical diffusion surface 16 with respect to the XY plane is preferably substantially 90°. Here, substantially perpendicular (substantially 90°) includes not only cases where it is perfectly perpendicular (90°), but also cases where it is within an error range that can be considered perpendicular (90°) (e.g., 90° ± 5°).

[0065] Furthermore, for example, due to manufacturing constraints on the protrusion 12, the vertical diffusion surface 16 may be inclined with respect to the XY plane, and the inclination angle β of the vertical diffusion surface 16 with respect to the XY plane may be less than 90°. The inclination angle β of the vertical diffusion surface 16 is preferably 70° or more, more preferably 80° or more, and even more preferably 85° or more. The larger the inclination angle β of the vertical diffusion surface 16 and the closer it is to 90°, the smaller the amount of protrusion (thickness D of the protrusion 12) of the protrusion 12 projecting in the Y direction from the rise surface 5 can be, thereby reducing the area of ​​the vertical diffusion surface 16 in an XY plane view. Therefore, the amount of light in the optical axis direction (Z direction) directly incident on the vertical diffusion surface 16 can be reduced, and the generation of noise light due to light directly incident on the vertical diffusion surface 16 can be suppressed.

[0066] The vertical diffusion surface 16 according to this embodiment is an arc-shaped curved surface, for example, a cylindrical lens surface with a circular arc. As shown in Figure 6, in the XY plane view of the convex portion 12 (cross-section obtained by cutting the vertical diffusion surface 16 with the XY plane), the boundary line 15 between the inclined diffusion surface 14 and the vertical diffusion surface 16 is an arc-shaped curved line. The vertical diffusion surface 16 consists of a cylindrical lens surface along the arc-shaped boundary line 15, and it is preferable that the curvature of the arc of the boundary line 15 is the same as the curvature of the cylindrical lens surface of the vertical diffusion surface 16. The axial direction of the cylindrical lens surface of this vertical diffusion surface 16 is parallel to the optical axis direction (Z direction) of the linear Fresnel lens 1. Note that the vertical diffusion surface 16 is not limited to the above example of an arc-shaped curved surface (cylindrical lens surface), and may be, for example, an elliptical arc-shaped curved surface, or a curved surface of other shapes.

[0067] As shown in Figure 7, in the XZ plan view of the convex portion 12, the vertical diffusion surface 16 occupies the portion of the rectangular area representing the outer shape of the convex portion 12 excluding the isosceles triangular area of ​​the inclined diffusion surface 14. In this XZ plan view, the vertical diffusion surface 16 has a pentagonal shape formed by combining five straight lines. The boundary line 15 between the inclined diffusion surface 14 and the vertical diffusion surface 16 is a V-shaped broken line. As shown in Figure 6, the vertical diffusion surface 16 protrudes most in the Y direction from the rise surface 5 at its central portion in the X direction (the position of the vertex of the V-shaped boundary line). The vertical diffusion surface 16 is a cylindrical convex curved surface in which the amount of protrusion decreases from the central portion in the X direction toward both sides.

[0068] As described above, the vertical diffusion surface 16 consists of, for example, a curved surface in the shape of an arc perpendicular to the XY plane (e.g., a cylindrical lens surface), and has a lens function that diffuses or focuses light. As a result, the vertical diffusion surface 16 has the effect of diffusing noise light incident on the vertical diffusion surface 16 in the curved direction. For example, a vertical diffusion surface 16 curved in the XY plane can diffuse noise light incident on the vertical diffusion surface 16 and disperse it in multiple directions within the XY plane (see Figure 10C).

[0069] [3.5. Dimensions of each part of a linear Fresnel lens] Here, the dimensions of each part of the linear Fresnel lens 1 according to this embodiment are given as an example. The uneven structure 10 formed on the rise surface 5 of the linear Fresnel lens 1 is a lens structure for diffusing noise light and has a size on the order of micrometers, for example. The dimensions of each part of the convex portion 12 constituting the uneven structure 10 and the dimensions of each part of the linear Fresnel lens 1 may be, for example, as follows.

[0070] H: Height of the protrusion 12 in the Z direction: 1 to 150 μm D: Thickness of the protrusion 12 in the Y direction (protrusion length of the protrusion 12): 1 to 500 μm P: Arrangement pitch of the protrusions 12 in the X direction (width of the protrusions 12 in the X direction): 1 to 500 μm H1: Height in the Z direction of the inclined diffusion surface 14: H1 = H - H2 H2: Height in the Z direction of vertical diffusion plane 16: 10-90% of H Py: Arrangement pitch in the Y direction of Fresnel lens surface 4: 1~1000 μm θ: Tilt angle of Fresnel lens surface 4: Greater than 0°, less than 90° θ': Inclination angle of rise surface 5: 45° or more, 90° or less α: Inclination angle of inclined diffusion surface 14: greater than 0°, less than 90° β: Inclination angle of vertical diffusion surface 16: 45° or more, 90° or less

[0071] If the dimensions of each part of the protrusions 12 of the uneven structure 10 are within the above-mentioned range, the protrusions 12 of the uneven structure 10 can effectively exhibit the noise light diffusion function and reduce the intensity of the noise light.

[0072] Furthermore, the height H1 in the Z direction of the inclined diffusion surface 14 may be greater than the height H2 in the Z direction of the vertical diffusion surface 16 (H1 > H2). This increases the area of ​​the inclined diffusion surface 14 on the surface of the protrusion 12, allowing the three-dimensional diffusion effect of noise light by the inclined diffusion surface 14 to be more effectively exerted.

[0073] [3.6. Diffusion effect due to uneven structure] Next, with reference to Figures 9 and 10, the noise light diffusion effect of the uneven structure 10 of the rise surface 5 in the linear Fresnel lens 1 according to the first embodiment will be described in detail. Figure 9 is a YZ cross-sectional view (Figure 9A) and an XY cross-sectional view (Figure 9B) showing the linear Fresnel lens structure 103 of a conventional linear Fresnel lens 100 (see Figure 3). Figure 10 is a YZ cross-sectional view (Figure 10A), an XY cross-sectional view at the height of the inclined diffusion surface 14 (Figure 10B), and an XY cross-sectional view at the height of the vertical diffusion surface 16 (Figure 10C) showing the linear Fresnel lens structure 3 of the linear Fresnel lens 1 according to the first embodiment.

[0074] As shown in Figure 9, in a conventional linear Fresnel lens 100, parallel light 50 incident in the optical axis direction (Z direction) is refracted by the Fresnel lens surface 104 and travels in the same direction as normal light 51. However, parallel light 50 incident into the lens from the tip of the Fresnel lens surface 104 travels toward the rise surface 5 and is reflected by the rise surface 5. Here, the rise surface 105 of the conventional linear Fresnel lens structure 103 is a flat surface (see Figure 3). Therefore, as shown in Figure 9, light incident into the lens from the tip of the Fresnel lens surface 104 is specularly reflected by the flat rise surface 105 and becomes noise light 52 that travels in a different direction from the normal light 51. In this case, the noise light 52 is reflected in the same direction in the YZ plane, as shown in Figure 9A, and is also reflected in the same direction in the XY plane, as shown in Figure 9B.

[0075] Thus, in a conventional linear Fresnel lens 100, light entering the lens from the tip of the Fresnel lens surface 104 is reflected three-dimensionally in the same direction by the flat rise surface 105, resulting in noise light 52 that travels in the same direction. Therefore, when the light emitted from the linear Fresnel lens 100 is projected onto the screen 62, the noise light 52 concentrates at a predetermined location, increasing the intensity of the noise light 52 (see Figure 4).

[0076] In contrast, in the linear Fresnel lens 1 according to the first embodiment, a recessed structure 10 is provided on the rise surface 5 of the linear Fresnel lens structure 3 (see Figures 5 to 8). This recessed structure 10 consists of a plurality of protrusions 12 arranged in the X direction, and each protrusion 12 has an inclined diffusion surface 14 and a vertical diffusion surface 16. Thus, the rise surface 5 of the linear Fresnel lens structure 103 according to the first embodiment is a recessed surface with a complex recessed pattern, and is excellent in its ability to diffuse light over a wide area.

[0077] Therefore, in the linear Fresnel lens structure 3 according to the first embodiment, as shown in Figure 10, light incident into the lens from the leading edge of the Fresnel lens surface 4 is directed toward the convex portion 12 of the uneven structure 10 formed on the rise surface 5, reflected by the convex portion 12 of the rise surface 105, and diffused in various directions.

[0078] For example, since the inclined diffusion surface 14 of the convex portion 12 is a curved surface that is either spherical or aspherical, as shown in Figure 10A, the noise light 52 reflected by the curved inclined diffusion surface 14 is reflected and diffused in various directions within the YZ plane. Also, as shown in Figure 10B, the noise light 52 reflected by the curved inclined diffusion surface 14 is reflected and diffused in various directions within the XY plane as well.

[0079] In addition, the vertical diffusion surface 16 of the convex portion 12 according to the first embodiment is made of a curved surface such as a cylindrical lens surface and is curved in an arc shape in the XY cross-section. Therefore, as shown in Figure 10C, the noise light 52 reflected by the vertical diffusion surface 16 is also reflected and diffused in various directions within the XY plane.

[0080] Due to the diffusing action of the inclined diffusing surface 14 and the vertical diffusing surface 16 described above, the noise light 52 reflected by the uneven structure 10 of the rise surface 5 is diffused and scattered over a wide area. Therefore, when the light emitted from the linear Fresnel lens 1 (including normal light 51 and noise light 52) ​​is projected onto the screen 62, the noise light 52 is dispersed rather than concentrated in a predetermined location, so the intensity of the noise light 52 can be sufficiently reduced.

[0081] [4. Configuration of the Fresnel lens according to the second embodiment] Next, the configuration of the linear Fresnel lens 1 according to the second embodiment of the present invention will be described with reference to Figures 11 to 14. Figures 11 to 14 are a perspective view, a plan view, a front view, and a side view, respectively, showing the linear Fresnel lens 1 according to the second embodiment.

[0082] [4.1. Basic Configuration of Fresnel Lenses] As shown in Figures 11 to 14, the linear Fresnel lens 1 according to the second embodiment differs from the linear Fresnel lens 1 according to the first embodiment (see Figures 5 to 8) in the shape of the protrusions 22 of the uneven structure 20 formed on the rise surface 5, while the other components are the same as in the first embodiment. Therefore, in the following description, the protrusions 22 of the uneven structure 20 according to the second embodiment will be described in detail, and redundant explanations of the other components will be omitted.

[0083] [4.2. Uneven structure of the rise surface] As shown in Figures 11 to 14, the linear Fresnel lens 1 according to the second embodiment is characterized in that a special uneven surface structure 20 is formed on the rise surface 5 of the linear Fresnel lens structure 3, and the rise surface 5 is an uneven surface rather than a flat surface. This uneven surface structure 20 on the rise surface 5 is composed of a repeating pattern of multiple protrusions 22 arranged in the X direction. This uneven surface structure 20 has the function of diffusing and scattering noise light generated on the rise surface 5 over a wide area. Due to the diffusion and scattering function of this uneven surface structure 20, the noise light can be dispersed over a wide area in the optical image projected from the linear Fresnel lens 1, thereby reducing the intensity of the noise light. Thus, the uneven surface structure 20 provided on the rise surface 5 according to the second embodiment functions as a noise light reduction structure.

[0084] The uneven surface structure 20 has a plurality of protrusions 22 that are repeatedly provided on the rise surface 5 along the X direction at a predetermined pitch P. The protrusions 22 are fine protrusions that project in the Y direction from the rise surface 5 (ideally a vertical surface perpendicular to the XY plane). The protrusions 22 have a shape that is symmetrical with respect to the X direction. From the viewpoint of facilitating the design and manufacture of the uneven surface structure 20, it is preferable that the plurality of protrusions 22 constituting the uneven surface structure 20 have the same shape as each other, but they may have different shapes. The pitch P of the protrusions 22 that are repeatedly arranged in the X direction corresponds to the width of one protrusion 22 in the X direction.

[0085] The convex portion 22 is formed over the entire height direction (Z direction) of the rise surface 5. That is, the height H of the convex portion 22 is approximately the same as the height of the rise surface 5. The upper part of the convex portion 22 in the Z direction is connected to the upper edge 4a of one of the two adjacent Fresnel lens surfaces 4, 4 in the Y direction, the first Fresnel lens surface 4. The lower part of the convex portion 22 in the Z direction is connected to the lower edge 4b ​​of the other of the two Fresnel lens surfaces 4, 4, the second Fresnel lens surface 4.

[0086] The protrusion 22 comprises at least one inclined diffusion surface 24 and at least two vertical diffusion surfaces 26. In other words, the surface of one protrusion 22 includes at least one inclined diffusion surface 24 and at least two vertical diffusion surfaces 26. The inclined diffusion surface 24 is provided on the upper side of the protrusion 22 and is an inclined surface that has the function of diffusing light (especially noise light). On the other hand, the vertical diffusion surfaces 26 are provided on the lower side of the protrusion 22 and are vertical surfaces that have the function of diffusing light. The configuration of the inclined diffusion surface 24 and the vertical diffusion surfaces 26 will be described in detail below.

[0087] [4.3. Inclined Diffusion Surface] The inclined diffusion surface 24 is an example of a first diffusion surface. The inclined diffusion surface 24 is an inclined surface provided on the upper part of the convex portion 22 in the Z direction, and forms the upper surface of the convex portion 22. The upper end of the inclined diffusion surface 24 is connected to the upper edge 4a of one of the adjacent Fresnel lens surfaces 4, 4 in the Y direction, which is the first Fresnel lens surface 4 (the right Fresnel lens surface 4 in Figure 14). The lower end of the inclined diffusion surface 24 is connected to the upper parts of the two vertical diffusion surfaces 26, 26.

[0088] The inclined diffusion surface 24 is an inclined surface that is inclined in the opposite direction to the Fresnel lens surface 4 with respect to the XY plane. For example, as shown in Figures 11 and 14, if the Fresnel lens surface 4 is inclined downwards in the positive direction of the Y, then the inclined diffusion surface 24 is inclined downwards in the negative direction of the Y.

[0089] The inclination angle α of the inclined diffusion surface 24 with respect to the XY plane (see Figure 11) is greater than 0° and less than 90°, preferably 60° or more, more preferably 70° or more, and even more preferably 80° or more. The larger the inclination angle α of the inclined diffusion surface 24 and the closer it is to 90°, the smaller the amount of protrusion (thickness D of the protrusion 22) of the convex portion 22 protruding in the Y direction from the rise surface 5 can be, thereby reducing the area of ​​the convex portion 22 (i.e., the area of ​​the inclined diffusion surface 24) in the XY plane view. Therefore, the amount of light in the optical axis direction (Z direction) that is directly incident on the inclined diffusion surface 24 can be reduced, and the generation of noise light due to light directly incident on the inclined diffusion surface 24 can be suppressed.

[0090] As shown in Figure 12, in the XY plan view of the convex portion 22, the inclined diffusion surface 24 has a planar shape of an isosceles triangle formed by combining three straight lines. In detail, the boundary line between the upper edge of the inclined diffusion surface 24 (the contour line of the upper end in the Z direction) and the upper edge 4a of the first Fresnel lens surface 4 is a straight line. Also, the boundary line 25 between the lower edge of the inclined diffusion surface 24 (the contour line of the lower end in the Z direction) and the two vertical diffusion surfaces 26, 26 is a broken line made up of two straight lines. As will be described later, since the two vertical diffusion surfaces 26, 26 of the convex portion 22 according to the second embodiment are flat surfaces, it is preferable that the boundary line 25 between the inclined diffusion surface 24 and the two vertical diffusion surfaces 26, 26 be a broken line made up of two straight lines. This allows the inclined diffusion surface 24 to be appropriately connected to the two vertical diffusion surfaces 26, 26 which are flat surfaces. Furthermore, the boundary line 25 between the inclined diffusion surface 24 and the vertical diffusion surface 26 is not limited to the example of an isosceles triangular polyline shown in Figure 12, but may also be a polyline of any polygonal shape with any number of vertices, such as a triangle, quadrilateral, pentagon, or octagon.

[0091] The gradient diffusion surface 24 may be a flat surface, or a curved surface that is spherical or aspherical. In the examples shown in Figures 11 to 14, the gradient diffusion surface 24 is a triangular flat surface. However, the example is not limited to this, and the gradient diffusion surface 24 may be, for example, a curved surface that is convex upwards, like a convex lens, or a curved surface that is convex downwards, like a concave lens. By forming the gradient diffusion surface 24 with a curved surface that is spherical or aspherical in this way, a lensing effect can be imparted to the gradient diffusion surface 24, thereby improving the diffusion effect of noise light by the gradient diffusion surface 24.

[0092] Thus, the gradient diffusion surface 24 is, for example, a flat or curved surface inclined at an angle α with respect to the XY plane. Such a gradient diffusion surface 24 can diffuse noise light incident on the gradient diffusion surface 24 and scatter it in multiple directions in the YZ plane and multiple directions in the XY plane (see Figures 15A and 15B). Therefore, since the noise light can be dispersed over a wide area by the gradient diffusion surface 24, the intensity of the noise light can be suitably reduced. Furthermore, even if the gradient diffusion surface 24 is a flat surface, the noise light can be diffused by the gradient diffusion surface 24 and the vertical diffusion surface 26, which have different inclination angles α and β, and dispersed two-dimensionally in multiple directions in the YZ plane and the XY plane.

[0093] [4.4. Vertical diffusion surface] The vertical diffusion surface 26 is an example of a second diffusion surface. The vertical diffusion surface 26 is a vertical surface provided on the lower side of the convex portion 22. The vertical diffusion surface 26 connects the lower edge 4b ​​of the other second Fresnel lens surface 4 (the Fresnel lens surface 4 on the left in Figure 8) of the two adjacent Fresnel lens surfaces 4, 4 in the Y direction, to the inclined diffusion surface 24. The lower end of the vertical diffusion surface 26 is connected to the lower edge 4b ​​of the second Fresnel lens surface 4. The upper end of the vertical diffusion surface 26 is connected to the lower end of the inclined diffusion surface 24. The boundary line 25 between the inclined diffusion surface 24 and the vertical diffusion surface 26 is a ridge line.

[0094] The vertical diffusion surface 26 is preferably substantially perpendicular to the XY plane. That is, the inclination angle β of the vertical diffusion surface 26 with respect to the XY plane is preferably substantially 90°. Here, substantially perpendicular (90°) includes not only cases where it is perfectly perpendicular (90°), but also cases where it is within an error range that can be considered perpendicular (90°) (e.g., 90° ± 5°).

[0095] Furthermore, due to manufacturing constraints on the protrusions 22, the vertical diffusion surface 26 may be inclined with respect to the XY plane, and the inclination angle β of the vertical diffusion surface 26 with respect to the XY plane may be less than 90° or 45° or more. The inclination angle β of the vertical diffusion surface 26 is preferably 70° or more, more preferably 80° or more, and even more preferably 85° or more. The larger the inclination angle β of the vertical diffusion surface 26 and the closer it is to 90°, the smaller the amount of protrusion (thickness D of the protrusions 22) of the protrusions 22 projecting in the Y direction from the rise surface 5 can be, thereby reducing the area of ​​the vertical diffusion surface 26 in an XY plane view. Therefore, the amount of light in the optical axis direction (Z direction) directly incident on the vertical diffusion surface 26 can be reduced, and the generation of noise light due to light directly incident on the vertical diffusion surface 26 can be suppressed.

[0096] In the first embodiment described above, as shown in Figures 5 to 8, the vertical diffusion surface 16 is composed of a single curved surface (cylindrical lens surface). In contrast, in the second embodiment, as shown in Figures 11 to 14, the vertical diffusion surface 26 is composed of, for example, a combination of two rectangular flat surfaces. Thus, it is also possible to configure the vertical diffusion surface 26 of the convex portion 22 not as a curved surface like the vertical diffusion surface 16 of the first embodiment, but as a combination of two or more flat surfaces. In the example of the convex portion 22 of the second embodiment, a vertical diffusion surface 26 consisting of a combination of two flat surfaces is provided to match the triangular inclined diffusion surface 24. However, the invention is not limited to this example, and when using an inclined diffusion surface 24 with a polygonal shape having n vertices, a vertical diffusion surface 26 consisting of n-1 flat surfaces may be provided to match the polygonal inclined diffusion surface 24. The larger the number of vertices n of the polygon of the inclined diffusion surface 24, the closer the convex surface formed by combining the n-1 flat surfaces of the vertical diffusion surface 26 becomes to a cylindrical surface, allowing light to be diffused in various directions. Therefore, n is preferably a larger integer than or equal to 3.

[0097] In the second embodiment, the vertical diffusion surface 26 is composed of, for example, a combination of flat surfaces, so the boundary line 25 between the inclined diffusion surface 24 and the vertical diffusion surface 26 is a polyline made up of a part of a polygon. More specifically, as shown in Figure 12, in the XY plane view of the convex portion 22 (cross-section obtained by cutting the vertical diffusion surface 26 with the XY plane), the boundary line 25 between the inclined diffusion surface 24 and the vertical diffusion surface 26 is a V-shaped polyline made up of a part of a triangle. Then, as shown in Figures 11 to 13, the two flat surfaces of the vertical diffusion surface 26 are arranged along the boundary line 25, which is a V-shaped polyline.

[0098] As described above, the vertical diffusion surface 26 of the convex portion 22 according to the second embodiment consists of, for example, a plurality of flat surfaces perpendicular to the XY plane. This vertical diffusion surface 26 is a convex surface formed by combining a plurality of flat surfaces along a broken line boundary line 25 which is part of a polygon. The convex vertical diffusion surface 26 formed by combining the plurality of flat surfaces can reflect or refract light in different directions. As a result, noise light incident on each flat surface of the vertical diffusion surface 26 is reflected in the reflection direction corresponding to the surface direction of each flat surface, and the vertical diffusion surface 26 as a whole has the effect of diffusing in multiple different directions. For example, the vertical diffusion surface 26 can reflect noise light incident on each flat surface in different directions and disperse it in multiple directions within the XY plane (see Figure 15C).

[0099] [4.5. Dimensions of each part of a linear Fresnel lens] The dimensions of each part of the protrusion 22 constituting the uneven structure 20 according to the second embodiment (for example, H, D, P, H1, H2, Py, θ, θ', α, β, etc.) are the same as the dimensions of each part of the protrusion 12 constituting the uneven structure 10 according to the first embodiment described above, so a detailed explanation is omitted.

[0100] [4.6. Diffusion effect due to uneven structure] Next, with reference to Figures 9 and 15, the noise light diffusion effect of the uneven structure 20 of the rise surface 5 in the linear Fresnel lens 1 according to the second embodiment will be described in detail. Figure 15 shows a YZ cross-sectional view (Figure 15A), an XY cross-sectional view at the height of the inclined diffusion surface 24 (Figure 15B), and an XY cross-sectional view at the height of the vertical diffusion surface 26 (Figure 15C) of the linear Fresnel lens structure 3 of the linear Fresnel lens 1 according to the second embodiment.

[0101] As shown in Figure 9 above, in a conventional linear Fresnel lens 100, light entering the lens from the tip of the Fresnel lens surface 104 is reflected three-dimensionally in the same direction by the flat rise surface 105, resulting in noise light 52 that travels in the same direction. Therefore, when the light emitted from the linear Fresnel lens 100 is projected onto the screen 62, the noise light 52 concentrates at a predetermined location, increasing the intensity of the noise light 52 (see Figure 4).

[0102] In contrast, in the linear Fresnel lens 1 according to the second embodiment, a surface uneven structure 20 is provided on the rise surface 5 of the linear Fresnel lens structure 3 (see Figures 11 to 14). This surface uneven structure 20 consists of a plurality of protrusions 22 arranged in the X direction, and each protrusion 22 has an inclined diffusion surface 24 and a vertical diffusion surface 26. Thus, the rise surface 5 of the linear Fresnel lens structure 103 according to the second embodiment is an uneven surface with a complex surface uneven pattern, and has excellent performance in diffusing light over a wide area.

[0103] Therefore, in the linear Fresnel lens structure 3 according to this embodiment, as shown in Figure 15, light incident into the lens from the leading edge of the Fresnel lens surface 4 is directed toward the convex portion 22 of the uneven structure 20 formed on the rise surface 5, reflected by the convex portion 22 of the rise surface 105, and diffused in various directions.

[0104] For example, since the inclined diffusion surface 24 (inclination angle α) and the vertical diffusion surface 26 (inclination angle β) of the convex portion 22 have different inclination angles (α < β), as shown in Figure 15A, the noise light 52 reflected by the upper inclined diffusion surface 24 in the Z direction and the noise light 52 reflected by the lower vertical diffusion surface 26 in the Z direction are reflected and diffused in different directions within the YZ plane. Also, as shown in Figure 15B, the noise light 52 reflected by the central inclined diffusion surface 24 in the X direction, the noise light 52 reflected by one vertical diffusion surface 26 in the X direction, and the noise light 52 reflected by the other vertical diffusion surface 26 in the X direction are reflected and diffused in different directions within the XY plane.

[0105] In addition, the vertical diffusion surface 26 of the convex portion 22 according to the second embodiment has a structure in which two flat surfaces are combined in a V-shape, so the plane directions of the two flat surfaces are different from each other. Therefore, as shown in Figure 15C, the noise light 52 reflected by one vertical diffusion surface 26 in the X direction and the noise light 52 reflected by the other vertical diffusion surface 26 in the X direction are reflected and diffused in different directions within the XY plane.

[0106] Due to the diffusion effect of the inclined diffusion surface 24 and the vertical diffusion surface 26 described above, the noise light 52 reflected by the uneven structure 20 of the rise surface 5 is diffused and scattered over a wide area. Therefore, when the light emitted from the linear Fresnel lens 1 (including normal light 51 and noise light 52) ​​is projected onto the screen 62, the noise light 52 is dispersed rather than concentrated in a predetermined location, thus allowing for an appropriate reduction in the intensity of the noise light 52.

[0107] [5. Manufacturing method of linear Fresnel lenses] Next, a method for manufacturing the linear Fresnel lens 1 according to the first and second embodiments described above will be explained.

[0108] As described above, the linear Fresnel lens 1 according to this embodiment has uneven structures 10 and 20 formed on the rise surface 5 of the linear Fresnel lens structure 3. The uneven structures 10 and 20 are structures in which a plurality of protrusions 12 and 22 are repeatedly arranged at a predetermined pitch P along the longitudinal direction (X direction) of the rise surface 5. Furthermore, the upper structure of the protrusions 12 and 22 in the optical axis direction (Z direction) (the part where the inclined diffusion surfaces 14 and 24 exist) does not overlap the lower structure (the part where the vertical diffusion surfaces 16 and 26 exist). In other words, the protrusions 12 and 22 according to this embodiment do not have a so-called undercut structure.

[0109] This makes it possible to manufacture the uneven structures 10 and 20 of the linear Fresnel lens 1 using a manufacturing method that forms the uneven structures 10 and 20 linearly from the front surface in the optical axis direction (Z direction) of the linear Fresnel lens 1, for example, by photolithography using a laser writing device or by machining. In other words, since the uneven structures 10 and 20 according to this embodiment do not include an undercut structure, the upper structure of the uneven structures 10 and 20 (the part where the inclined diffusion surfaces 14 and 24 exist) does not hinder the formation of the lower structure (the part where the vertical diffusion surfaces 16 and 26 exist). Therefore, the uneven structures 10 and 20 of the linear Fresnel lens structure 3 can be easily and accurately formed from the front side in the optical axis direction (Z direction) of the linear Fresnel lens 1 using a manufacturing method such as photolithography using a laser writing device or by machining.

[0110] Furthermore, the linear Fresnel lens 1 according to this embodiment can be manufactured by methods such as electron beam lithography, photolithography, cutting, or mold molding. If the linear Fresnel lens structure 3 is designed such that the dimensions of the convex portions 12 and 22, such as the height H in the Z direction and the width (pitch P) in the X direction, the radius of curvature of the arc of the boundary line 15 of the inclined diffusion surface 14 of the convex portion 12, and the arrangement pitch Py of the Fresnel lens surface 4, are within the range of 1 to 100 μm, then the linear Fresnel lens structure 3 can be manufactured by, for example, electron beam lithography or photolithography. On the other hand, if these dimensions exceed 100 μm, then the linear Fresnel lens structure 3 can be manufactured by, for example, cutting or mold molding.

[0111] As described above, according to the uneven structures 10 and 20 formed on the rise surface 5 of the linear Fresnel lens structure 3 according to this embodiment, the repeating structure of the multiple protrusions 12 and 22 is unfolded on the XY plane in a manner that allows access from the front side in the optical axis direction (Z direction), and does not have an undercut structure like the uneven surface formed on the rise surface in Patent Document 1. Therefore, the linear Fresnel lens structure 3 can be easily and accurately formed by photolithography using a laser writing device or by cutting. Thus, no special equipment or tools are required to manufacture the linear Fresnel lens structure 3 according to this embodiment, and the manufacturing process is not complicated.

[0112] Furthermore, according to the manufacturing method of the linear Fresnel lens structure 3 of this embodiment, the coating step of the light-absorbing layer on the rise surface can be omitted, as described in Patent Document 2. Moreover, there is no need to deal with manufacturing issues arising from the coating of the light-absorbing layer (for example, paint overflowing from the rise surface onto the Fresnel lens surface, insufficient coating of paint on the rise surface, etc.).

[0113] [6. Summary] As described above, according to the linear Fresnel lens 1 of the first and second embodiments described above, the rise surface 5 of the linear Fresnel lens structure 3 is provided with uneven structures 10 and 20. The uneven structures 10 and 20 comprise a plurality of protrusions 12 and 22 that are repeatedly arranged along the X direction at a predetermined pitch P. The protrusions 12 and 22 are convex structures that project from the rise surface 5 in the Y direction. The rise surface 5 according to this embodiment is an uneven surface consisting of a plurality of protrusions 12 and 22, and this uneven surface connects two adjacent Fresnel lens surfaces 4 and 4 in the Y direction. The upper part of the protrusions 12 and 22 in the Z direction is provided with inclined diffusion surfaces 14 and 24 that are connected to the upper edge 4a of one of the Fresnel lens surfaces 4. The inclined diffusion surfaces 14 and 24 have the function of diffusing light three-dimensionally (in directions within the YZ plane and XY plane). The lower part of the protrusions 12 and 22 in the Z direction is provided with vertical diffusion surfaces 16 and 26 that are connected to the lower edge 4b ​​of the other Fresnel lens surface 4. The vertical diffusion surfaces 16 and 26 have the function of connecting the inclined diffusion surfaces 14 and 24 with the other Fresnel lens surface 4 and the function of diffusing light two-dimensionally (in the direction within the XY plane). The inclination angle α of the inclined diffusion surfaces 14 and 24 with respect to the XY plane and the inclination angle β of the vertical diffusion surfaces 16 and 26 are different angles, with the inclination angle β being greater than the inclination angle α. Thus, in the linear Fresnel lens structure 3 according to the first and second embodiments, a plurality of inclined diffusion surfaces 14 and 24 are repeatedly provided on the upper part of the rise surface 5 along the X direction at a predetermined pitch P, and a plurality of vertical diffusion surfaces 16 and 26 are repeatedly provided on the lower part of the rise surface 5 along the X direction at a predetermined pitch P.

[0114] With this configuration, noise light incident on the upper part of the rise surface 5 (internal light traveling inside the lens, or external light incident from outside the lens) can be diffused in multiple directions by the inclined diffusion surfaces 14 and 24, scattering over a wide area. Therefore, the intensity of noise light in the optical image projected from the linear Fresnel lens 1 can be reduced. In this way, by scattering the noise light, the noise light that was conventionally concentrated in a certain area on the screen 62 (see Figure 4) can be dispersed over a wide area, and the intensity of the noise light can be suitably reduced.

[0115] Furthermore, the inclined diffusion surfaces 14, 24 and the vertical diffusion surfaces 16, 26, which are arranged at different inclination angles α and β, can diffuse the incident light in at least multiple directions within the YZ plane. For example, as shown in Figures 10A and 15A, the inclined diffusion surfaces 14, 24 and the vertical diffusion surfaces 16, 26 can reflect the internal light incident from the leading edge of the Fresnel lens surface 4 and traveling through the linear Fresnel lens 1 in multiple directions within the YZ plane, thereby diffusing it in multiple directions within that YZ plane.

[0116] Furthermore, if the inclined diffusion surfaces 14 and 24 are curved surfaces, the light incident on the inclined diffusion surfaces 14 and 24 can be diffused in multiple directions within the YZ plane and multiple directions within the XY plane. For example, as shown in Figure 10A, the inclined diffusion surface 14 can reflect the internal light (noise light 52) ​​incident from the tip of the Fresnel lens surface 4 and traveling through the linear Fresnel lens 1 in multiple directions within the YZ plane, thereby diffusing it in multiple directions within the YZ plane. Furthermore, as shown in Figure 10B, the inclined diffusion surface 14 can reflect the internal light (noise light 52) ​​in multiple directions within the XY plane, thereby diffusing it in multiple directions within the XY plane.

[0117] Therefore, in order to enhance the diffusion effect of noise light by the inclined diffusion surfaces 14 and 24, it is preferable that the inclined diffusion surfaces 14 and 24 consist of spherical or aspherical curved surfaces, and more preferably convex lens-like curved surfaces. This allows the inclined diffusion surfaces 14 and 24 to diffuse the noise light incident on them three-dimensionally in various directions. Consequently, the noise light can be scattered over a wide area by the inclined diffusion surfaces 14 and 24, and the intensity of the noise light can be sufficiently reduced.

[0118] Furthermore, since the vertical diffusion surface 16 of the convex portion 12 according to the first embodiment is a curved surface such as a cylindrical lens surface, the light incident on the vertical diffusion surface 16 can be diffused in multiple directions within the XY plane. For example, as shown in Figure 10C, the vertical diffusion surface 16 can reflect internal light (noise light 52) ​​that is incident from the tip of the Fresnel lens surface 4 and travels through the linear Fresnel lens 1 in multiple directions within the XY plane, thereby diffusing it in multiple directions within the XY plane. In this way, in the uneven structure 10 according to the first embodiment, the noise light diffusion effect can be exerted not only by the inclined diffusion surface 14 but also by the vertical diffusion surface 16, so the intensity of the noise light can be reduced more effectively.

[0119] Therefore, in order to enhance the noise light diffusion effect of the vertical diffusion surface 16 according to the first embodiment, it is preferable that the boundary line 15 between the inclined diffusion surface 14 and the vertical diffusion surface 16 is an arc-shaped curved line, and that the vertical diffusion surface 16 consists of a cylindrical lens surface along this arc-shaped curved line. This allows the vertical diffusion surface 16 to diffuse the noise light incident on the vertical diffusion surface 16 two-dimensionally in various directions. Thus, the noise light can be scattered by the vertical diffusion surface 16, and the intensity of the noise light can be suitably reduced.

[0120] Furthermore, in the convex portion 22 according to the second embodiment, the boundary line 25 between the inclined diffusion surface 24 and the vertical diffusion surface 26 is a broken line consisting of a part of a polygon (for example, a triangle). The convex portion 22 is equipped with a vertical diffusion surface 26 consisting of a plurality of flat surfaces, and the vertical diffusion surface 26 is a convex surface formed by combining a plurality of flat surfaces along the broken line boundary line 25. Such a vertical diffusion surface 26 can diffuse light incident on the plurality of flat surfaces of the vertical diffusion surface 26 in multiple directions in the XY plane. For example, as shown in Figure 15C, the vertical diffusion surface 26 can reflect internal light (noise light 52) ​​incident from the tip of the Fresnel lens surface 4 and traveling through the linear Fresnel lens 1 in multiple directions in the XY plane, thereby diffusing it in multiple directions in the XY plane. Thus, in the uneven structure 20 according to the second embodiment, the noise light diffusion effect can be exerted not only by the inclined diffusion surface 24 but also by the vertical diffusion surface 26, so the intensity of the noise light can be reduced more effectively.

[0121] Furthermore, it is preferable that the vertical diffusion surfaces 16 and 26 in this embodiment are substantially perpendicular to the XY plane. This minimizes the area of ​​the vertical diffusion surfaces 16 and 26 in the XY plane view, thereby suppressing direct incidence of light in the optical axis direction (Z direction) onto the vertical diffusion surfaces 16 and 26. Thus, the generation of noise light caused by direct incidence of incident light onto the vertical diffusion surfaces 16 and 26 can be suppressed.

[0122] Furthermore, it is preferable that the inclination angle α of the inclined diffusion surfaces 14 and 24 according to this embodiment is greater than the inclination angle θ of the Fresnel lens surface 4. This makes it possible to make the area of ​​the inclined diffusion surfaces 14 and 24 in the XY plane view sufficiently smaller compared to the area of ​​the Fresnel lens surface 4. Therefore, it is possible to suppress the direct incidence of light in the optical axis direction (Z direction) onto the inclined diffusion surfaces 14 and 24. Thus, it is possible to suppress the generation of noise light caused by the direct incidence of incident light onto the inclined diffusion surface 14.

[0123] Furthermore, as shown in Figure 1, the linear Fresnel lens 1 according to this embodiment may include a prism sheet with a prism structure as the linear Fresnel lens structure 3, and the multiple Fresnel lens surfaces 4 of the prism structure may be planes inclined at substantially the same inclination angle θ. This makes it possible to provide a prism sheet that can reduce the intensity of noise light as an example of the linear Fresnel lens 1. [Examples]

[0124] Next, a linear Fresnel lens according to an embodiment of the present invention will be described. It should be noted that the following embodiment is merely an example to demonstrate the effects and feasibility of the linear Fresnel lens according to the present invention, and the present invention is not limited to the following embodiment.

[0125] As Example 1, a linear Fresnel lens 1 according to the first embodiment (see Figures 5 to 8) was manufactured. As Example 2, a linear Fresnel lens 1 according to the second embodiment (see Figures 11 to 14) was manufactured. Then, as shown in Figure 4, a simulation was performed to measure the light intensity distribution when parallel light 50 emitted from a light source 60 was projected onto a screen 62 through the linear Fresnel lenses 1 according to Examples 1 and 2.

[0126] Furthermore, as comparative examples, a linear Fresnel lens 100 according to Comparative Example 1 (see Figure 16), a linear Fresnel lens 200 according to Comparative Example 2 (see Figure 17), and a linear Fresnel lens 300 according to Comparative Example 3 (see Figure 18) were manufactured, and simulations were performed under the same conditions as in Examples 1 and 2.

[0127] [1. Test Conditions] As the light source 60, a surface light source capable of emitting rectangular parallel light 50 was used. The details of the light source 60 are as follows. Wavelength: 450nm Light distribution: Parallel light Shape: Rectangle Size: 0.2 x 0.2 mm Strength: 1W

[0128] Furthermore, the basic conditions for the linear Fresnel lenses in Examples 1 and 2 and Comparative Examples 1 to 3 were as follows. Shape: rectangular plate Size: 0.9 x 0.9 mm Base material thickness: 0.2mm Material: Triacetylcellulose Refractive index: 1.48 The arrangement pitch Py of the Fresnel lens surface in the Y direction is 0.125 mm. Z-direction height of the Fresnel lens surface (depth of the sawtooth groove): 0.1 mm Fresnel lens surface inclination angle θ: 32.62° Rise surface inclination angle θ': 90°

[0129] [Comparative Example 1] As shown in Figure 16, the linear Fresnel lens 100 according to Comparative Example 1 has a linear Fresnel lens structure 103 similar to the conventional linear Fresnel lens 100 described above (see Figure 3). The linear Fresnel lens structure 103 according to Comparative Example 1 is a prism structure in which a plurality of Fresnel lens surfaces 104 and a plurality of rise surfaces 105 are arranged alternately. The rise surface 105 according to Comparative Example 1 is a flat surface perpendicular to the XY plane.

[0130] [Comparative Example 2] As shown in Figure 17, the linear Fresnel lens 200 according to Comparative Example 2 has a linear Fresnel lens structure 203 corresponding to the Fresnel lens of Patent Document 1 (Japanese Patent Application Publication No. 2003-177217). The linear Fresnel lens structure 203 according to Comparative Example 2 is a prism structure in which a plurality of Fresnel lens surfaces 204 and a plurality of rise surfaces 205 are arranged alternately. The rise surface 205 according to Comparative Example 2 has an uneven surface similar to the uneven surface of the rise surface described in Patent Document 1, and an uneven structure 210 is provided on the rise surface 205. This uneven structure 210 of the rise surface 205 is constructed by arranging small corner cubes closely together in the height direction (Z direction) and consists of three grooves extending along the longitudinal direction (X direction) of the rise surface 205. The height difference between the protrusions and grooves of the uneven structure 210 is 0.01 mm.

[0131] [Comparative Example 3] As shown in Figure 18, the linear Fresnel lens 200 according to Comparative Example 3 has a linear Fresnel lens structure 303 corresponding to the Fresnel lens of Patent Document 2 (Japanese Patent Application Publication No. 2002-49100). The linear Fresnel lens structure 303 according to Comparative Example 3 is a prism structure in which a plurality of Fresnel lens surfaces 204 and a plurality of rise surfaces 305 are arranged alternately. The rise surfaces 305 according to Comparative Example 3 are coated with a light-absorbing layer 310 for absorbing unwanted light. The material of the light-absorbing layer 310 is ABSORB, the thickness of the light-absorbing layer 310 is 0.01 mm, and the light absorption rate of the light-absorbing layer 310 (set value in simulation) is 100%.

[0132] [Example 1] The linear Fresnel lens 1 according to Example 1 has a linear Fresnel lens structure 3 corresponding to the linear Fresnel lens 1 according to the first embodiment described above (see Figures 5 to 8). The linear Fresnel lens structure 3 according to Example 1 is a prism structure in which a plurality of Fresnel lens surfaces 4 and a plurality of rise surfaces 5 are arranged alternately. As shown in Figures 5 to 8, a recessed structure 10 is formed on the rise surface 5 according to Example 1, and the recessed structure 10 has a plurality of protrusions 12 repeatedly arranged along the longitudinal direction (X direction) at a predetermined pitch P. The protrusions 12 include a spherical inclined diffusion surface 14 and a cylindrical lens surface 16. As shown in Figure 6, the boundary line 15 between the inclined diffusion surface 14 and the vertical diffusion surface 16 in the XY plane view is arc-shaped.

[0133] [Example 2] The linear Fresnel lens 1 according to Example 2 has a linear Fresnel lens structure 3 corresponding to the linear Fresnel lens 1 according to the second embodiment described above (see Figures 11 to 14). The linear Fresnel lens structure 3 according to Example 2 is a prism structure in which a plurality of Fresnel lens surfaces 4 and a plurality of rise surfaces 5 are arranged alternately. As shown in Figures 11 to 14, a recessed structure 20 is formed on the rise surface 5 according to Example 2, and the recessed structure 20 has a plurality of protrusions 22 repeatedly arranged along the longitudinal direction (X direction) at a predetermined pitch P. The protrusions 22 include an inclined diffusion surface 24 made of a flat surface and a vertical diffusion surface 26 formed by combining two flat surfaces in a V shape. As shown in Figure 12, the boundary line 25 between the inclined diffusion surface 24 and the vertical diffusion surface 26 in an XY plane view is V-shaped, consisting of two sides of an isosceles triangle.

[0134] The dimensions of the convex portions 12 and 22 of the convex and concave structures 10 and 20 of the linear Fresnel lens 1 according to Example 1 and Example 2 are as follows.

[0135] H: Height of protrusions 12 and 22 in the Z direction: 0.1 mm D: Thickness of protrusions 12 and 22 in the Y direction (protrusion length of protrusions 12 and 22): 0.0125 mm P: Alignment pitch of protrusions 12 and 22 in the X direction (width of protrusion 12 in the X direction): 0.1 mm H1: Z-direction height of inclined diffusion surfaces 14 and 24: 0.04 mm H2: Z-direction height of vertical diffusion surfaces 16 and 26: 0.06 mm α: Inclination angle of inclined diffusion surfaces 14 and 24: 78.95° β: Inclination angle of vertical diffusion surfaces 16 and 26: 90°

[0136] [2. Evaluation Results] Simulations were conducted to measure the light intensity distribution when parallel light from a light source was projected onto a screen 62 using the linear Fresnel lenses 100, 200, and 300 from Comparative Examples 1 to 3 and the linear Fresnel lens 1 from Examples 1 and 2. Figures 19 to 23 are photographs showing the simulation results of the light intensity distribution for Comparative Examples 1 to 3 and Examples 1 and 2, respectively.

[0137] As shown in Figure 19, in Comparative Example 1, three linear noise lights 52 appeared with high intensity on the screen 62 onto which the optical image emitted from the linear Fresnel lens 100 was projected, in a location away from the rectangular area of ​​normal light 51. The maximum intensity of the noise light 52 in Comparative Example 1 was 515 W / cm². 2 This was the case. The reason for this is thought to be as follows:

[0138] In the linear Fresnel lens 100 according to Comparative Example 1, as shown in Figures 3, 4, and 9, some of the parallel light incident on the leading edge of the Fresnel lens surface 104 is specularly reflected by the flat rise surface 105, becoming noise light 52 that travels in the same direction. Therefore, in the optical image projected from the linear Fresnel lens 100 onto the screen 62, as shown in Figure 19, the noise light 52 is concentrated on three linear points, resulting in a very high intensity of noise light 52, which is thought to be the cause of the prominent noise light 52.

[0139] Furthermore, as shown in Figure 20, in Comparative Example 2, approximately five linear noise lights 52 appeared at a relatively high intensity in a location away from the rectangular area of ​​normal light 51. Although the intensity of the noise light 52 in Comparative Example 2 was lower than that of Comparative Example 1, it was significantly higher than that of Examples 1 and 2, which will be described later. The maximum intensity of the noise light 52 in Comparative Example 2 was 172 W / cm². 2 This was the case. The reason for this is thought to be as follows:

[0140] In Comparative Example 2, the rise surface 205 of the linear Fresnel lens 200 has an uneven structure 210 formed thereon. While this uneven structure 210 can suppress to some extent the leakage of noise light 52 from the rise surface 205, it cannot completely confine the noise light 52 within the lens. Therefore, the noise light 52 that leaks out from the linear Fresnel lens 200 is concentrated and emitted in a specific direction, and the intensity of the noise light 52 in the projected optical image is still considered to be high.

[0141] Furthermore, as shown in Figure 21, in Comparative Example 3, three linear noise lights 52 appeared with high intensity in a location away from the rectangular area of ​​normal light 51. The intensity of the noise light 52 in Comparative Example 3 was slightly lower than that of Comparative Example 1, but significantly higher than that of Examples 1 and 2, which will be described later. The maximum intensity of the noise light 52 in Comparative Example 3 was 515 W / cm². 2 This was the case. The reason for this is thought to be as follows:

[0142] In Comparative Example 3, the rise surface 305 of the linear Fresnel lens 300 is coated with a light-absorbing layer 310. This light-absorbing layer 310 can suppress, to some extent, the leakage of noise light 52 from the rise surface 305. However, the light-absorbing layer 310 cannot sufficiently suppress the leakage of noise light 52 from the rise surface 305, and the noise light that leaks from the rise surface 305 is concentrated and emitted in a specific direction. Furthermore, even if the rise surface 305 is coated with the light-absorbing layer 310, light incident on the rise surface 305 beyond the critical angle undergoes total internal reflection and remains as noise light 52. For this reason, it is considered that the intensity of noise light 52 in the projected optical image of Comparative Example 23 is still considerably high. Thus, in Comparative Example 1 and Comparative Example 3, the noise light is mainly caused by total internal reflection within the rise surfaces 105 and 305, so the light-absorbing layer 310 does not function at all, and it is considered that the maximum intensity of noise light 52 is similar between Comparative Example 1 and Comparative Example 3.

[0143] In contrast, as shown in Figure 22, in Example 1, although a small amount of noise light 52 remains, the irradiation position of the noise light 52 is dispersed over a wide area. As a result, the noise light 52 is at a level that is almost invisible, and the intensity of the noise light 52 is significantly reduced. The maximum intensity of the noise light 52 in Example 1 is 62 W / cm². 2 The maximum intensity of noise light 52 in Comparative Examples 1 and 3 is 515 W / cm². 2 ) was significantly reduced to about 12% or less, and the maximum intensity of noise light 52 in Comparative Example 2 (172 W / cm²) was significantly reduced. 2 This was significantly reduced to approximately 36% or less compared to the previous level.

[0144] Furthermore, as shown in Figure 23, in Example 2, although the noise light 52 remains in the form of 4 × 8 small dots, the irradiation position of the noise light 52 is dispersed over a wide area, and the intensity of the noise light 52 is significantly suppressed. The maximum intensity of the noise light 52 in Example 2 was 432 W / cm². 2 The maximum intensity of noise light 52 in Comparative Examples 1 and 3 is 515 W / cm². 2 This was reduced to approximately 84% or less compared to the previous level.

[0145] The results of the above-described examples 1 and 2 demonstrate that by providing the uneven structures 10 and 20 on the rise surface 5 of the linear Fresnel lens structure 3, the noise light 52 incident on the rise surface 5 can be diffused in multiple directions and scattered over a wide area, thereby significantly reducing the intensity of the noise light 52 in the optical image projected onto the screen 62. In particular, as in Example 1, it was demonstrated that by providing a convex portion 12 that combines a spherical convex lens-like inclined diffusion surface 14 and a vertical diffusion surface 16 consisting of a cylindrical lens surface, the intensity of the noise light 52 can be significantly reduced.

[0146] Furthermore, it was confirmed that the linear Fresnel lens 1 according to Examples 1 and 2 also has manufacturing advantages compared to the linear Fresnel lenses 200 and 300 according to Comparative Examples 2 and 3.

[0147] In other words, the linear Fresnel lens 200 according to Comparative Example 2 has an undercut structure in the uneven structure 210 formed on the rise surface 205, as shown in the enlarged view of Figure 17. Therefore, it is difficult to form the uneven structure 210 as designed by photolithography or cutting, and there is a problem that it is not possible to form a more detailed uneven structure.

[0148] In contrast, the uneven structures 10 and 20 of the rise surface 5 in Examples 1 and 2 do not have an undercut structure. Therefore, when a specific molding method (e.g., photolithography or cutting) is used to linearly form the uneven structures 10 and 20 from the front side in the optical axis direction (Z direction) of the linear Fresnel lens 1, the upper structure of the uneven structures 10 and 20 does not hinder the formation of the lower structure. Thus, it has been confirmed that the uneven structures 10 and 20 of the rise surface 5 can be easily and accurately formed from the front side in the optical axis direction of the linear Fresnel lens 1 using a specific molding method such as photolithography or cutting.

[0149] Furthermore, the linear Fresnel lens 300 according to Comparative Example 3 has a problem in that, as shown in the enlarged view of Figure 18, the paint of the light-absorbing layer 310 applied to the base of the rise surface 305 may spill onto the Fresnel lens surface 304, or there may be insufficient application of the light-absorbing layer 310 to the tip of the rise surface 305, resulting in manufacturing defects and a decrease in optical performance of the linear Fresnel lens 300.

[0150] In contrast, the linear Fresnel lens 1 according to Examples 1 and 2 does not use a light-absorbing layer 310 like that in Comparative Example 3, and does not require the application of a separate material to the linear Fresnel lens structure 3. Therefore, manufacturing defects due to the application of a separate material and a decrease in optical performance do not occur. Thus, it was confirmed that the linear Fresnel lens 1 according to Examples 1 and 2 can be manufactured easily and with high precision without causing manufacturing defects or a decrease in optical performance, compared to the linear Fresnel lens 300 according to Comparative Example 3.

[0151] Embodiments of the present invention have been described above with reference to the attached drawings, but it goes without saying that the present invention is not limited to these embodiments. It is clear to those skilled in the art that various modifications or alterations can be conceived within the scope of the claims, and these will naturally also fall within the technical scope of the present invention.

[0152] For example, in the above embodiment, the protrusions 12 and 22 of the uneven structures 10 and 20 had inclined diffusion surfaces 14 and 24 (first diffusion surfaces) and vertical diffusion surfaces 16 and 26 (second diffusion surfaces), but they may also have other surfaces (for example, a third diffusion surface).

[0153] Furthermore, in the above embodiment, the multiple protrusions 12 and 22 of the uneven structures 10 and 20 were arranged at a uniform pitch P in the longitudinal direction (X direction) of the rise surface 5, but the invention is not limited to this example. For example, the protrusions 12 and 22 may be arranged at an uneven pitch in the longitudinal direction (X direction) of the rise surface 5. Also, in the above embodiment, the multiple protrusions 12 and 22 were arranged without gaps in the longitudinal direction (X direction) of the rise surface 5, but the invention is not limited to this example. For example, the multiple protrusions 12 and 22 may be arranged with gaps in the longitudinal direction (X direction) of the rise surface 5.

[0154] Furthermore, in the above embodiment, the protrusions 12 and 22 have a shape that is symmetrical with respect to the longitudinal direction (X direction) of the rise surface 5, so that a uniform diffusion effect can be exerted in the X direction. However, the embodiment is not limited to this example. For example, the protrusions 12 and 22 may have a shape that is asymmetrical with respect to the longitudinal direction (X direction) of the rise surface 5. [Explanation of symbols]

[0155] 1. Linear Fresnel lens 2 Base material 3. Linear Fresnel lens structure 4 Fresnel lens surface 5. Rise surface 10, 20 uneven structure 12, 22 Convex part 14, 24 Inclined diffusion surface (first diffusion surface) 15, 25 Boundary line 16, 26 Vertical diffusion plane (second diffusion plane) 50 Parallel light (incident light) 51 Normal light 52 Noise Light 60 light source 62 screens

Claims

1. Substrate and A linear Fresnel lens structure formed on at least one surface of the substrate, Equipped with, Assuming the surface of the substrate is the XY plane and the thickness direction of the substrate is the Z direction, The linear Fresnel lens structure described above is Multiple Fresnel lens surfaces extending along the X direction and arranged in the Y direction, An uneven structure formed on the rise surface connecting adjacent Fresnel lens surfaces in the Y direction, Includes, The aforementioned uneven structure has a plurality of protrusions that are repeatedly provided on the rise surface at a predetermined pitch along the X direction, The aforementioned protrusion is, A first diffusion surface is connected to the upper edge of one of the adjacent Fresnel lens surfaces in the Y direction and is inclined with respect to the XY plane, A second diffusion surface connecting the lower edge of the other second Fresnel lens surface among the adjacent Fresnel lens surfaces in the Y direction and the first diffusion surface, A linear Fresnel lens, including one.

2. The linear Fresnel lens according to claim 1, wherein the first diffusing surface diffuses light incident on the first diffusing surface in at least multiple directions in the YZ plane.

3. The linear Fresnel lens according to claim 2, wherein the first diffusing surface diffuses light incident on the first diffusing surface in multiple directions in the YZ plane and in multiple directions in the XY plane.

4. The linear Fresnel lens according to any one of claims 1 to 3, wherein the first diffusion surface is a spherical or aspherical curved surface.

5. The linear Fresnel lens according to claim 4, wherein the first diffusion surface is a curved surface like a convex lens.

6. The linear Fresnel lens according to any one of claims 1 to 3, wherein the second diffusing surface diffuses light incident on the second diffusing surface in multiple directions within the XY plane.

7. The boundary line between the first diffusion surface and the second diffusion surface is an arc-shaped curved line. The linear Fresnel lens according to any one of claims 1 to 3, wherein the second diffusion surface consists of a cylindrical lens surface along the arc-shaped curve.

8. The boundary line between the first diffusion surface and the second diffusion surface is a broken line consisting of a part of a polygon. The linear Fresnel lens according to any one of claims 1 to 3, wherein the second diffusion surface consists of a convex surface formed by combining a plurality of flat surfaces along the broken line.

9. A linear Fresnel lens according to any one of claims 1 to 3, wherein the inclination angle of the first diffusion surface with respect to the XY plane is greater than the inclination angle of the Fresnel lens surface with respect to the XY plane.

10. The linear Fresnel lens includes a prism sheet having a prism structure as the linear Fresnel lens structure, The linear Fresnel lens according to any one of claims 1 to 3, wherein the plurality of Fresnel lens surfaces of the prism structure are planes inclined at substantially the same angle of inclination.

Images